This proposal describes a four-year basic science training program for the development of a career in academic Pediatric Gastroenterology. The principal investigator, Dr. Elizabeth A. Marcus, a Clinical Instructor in Pediatric Gastroenterolog at the University of California, Los Angeles with a projected title of Assistant Professor as of 7/1/13, is board-certified in General Pediatrics and Pediatric Gastroenterology. She completed Pediatrics residency at Children's Hospital Los Angeles. She participated in basic science research, studying the acid acclimation mechanisms and bacterial physiology of the gastric pathogen Helicobacter pylori throughout medical school, residency, and fellowship. The current proposal incorporates a newly developed and divergent research focus, studying the effect of the bacteria and acidic pH on the gastric mucosa. The program outlined in this proposal will provide the applicant with an excellent research environment and protected time to attain the skills needed to achieve her goal of becoming an independent investigator. The mentor, Dr. George Sachs, is a recognized expert in gastric physiology, acid secretion, and bacterial factors associated with H. pylori acid acclimation. Dr. Sachs has a strong history of mentoring graduate students and postdoctoral fellows who have progressed to become independent investigators. Co-mentor Dr. David Scott will contribute expertise on H. pylori, microscopy, animal models, and eukaryotic cell systems. Co-mentor Dr. Charalabos Pothoulakis will provide expertise on inflammation and mucosal immunology. An advisory committee will monitor career development and provide additional training in immunology, mass spectrometry and epithelial physiology. The Department of Pediatrics has already committed 75% protected research time to the applicant. UCLA provides a rich research and academic environment that will foster the development of research independence. The proposed research focuses on how H. pylori, in coordination with gastric acidity, is able to injure the gastric mucosa and trigger development of advanced disease. H. pylori infection is highly prevalent worldwide and at a minimum causes gastric inflammation. Some of those infected progress to develop gastric or duodenal ulcer disease, gastric atrophy, and cancer. Treatment is becoming more difficult with emerging antibiotic resistance and problems with patient compliance with a complex treatment regimen. It is not definitively known how the bacteria are able to evade the immune system, leading to lifelong infection, or what factors contribute to development of advanced disease, although multiple bacterial and host factors have been studied. This proposal will use in vitro and in vivo model systems with physiologic similarities to the host environment to determine epithelial changes and alterations in immune response. Quantitative mass spectrometry using SILAC (Stable Isotope Labeling by Amino acids in Cell culture) technology will be used to study protein changes in the cell junction in response first to acidity, then to H. pylori infection. Candidate proteins or pathways will be inhibited to confirm involvement. Confocal microscopy will be used to further study the cell junctions in co-culture with acidic pH. Cell layer resistance and permeability changes will be characterized. Mediators involved with the Th1 and Th17 immune responses will be studied in the context of H. pylori infection and acidic pH. H. pylori genes with increased expression in acid and in a gerbil model will be studied as potential modulators of immune response. Potent acid inhibition with a novel acid blocker in infected gerbils will be employed to determine the effect on bacterial load, inflammatory infiltrate, and cytokine production. It is anticipated that this work will add to the understanding of the mechanisms of gastric injury and will lead to development of novel treatment targets for both the infection and its short and long term consequences to the host.